Prior calcite precipitation and source mixing process influence Sr/Ca, Ba/Ca and 87Sr/86Sr of a stalagmite developed in southwestern Japan during 18.0 4.5ka

Abstract We measured Sr/Ca, Ba/Ca, 87 Sr/ 86 Sr ratios, δ 18 O and δ 13 C values in a stalagmite, which developed 18.0–4.5 thousand years ago (ka) in southwestern Japan. Dripwater and two major bedrocks (limestone and andesite) in the locality were also studied. The 87 Sr/ 86 Sr ratios of the stalagmite are relatively homogeneous (0.706852–0.706921), suggesting a steady source mixing ratio of ~ 40% from high- 87 Sr/ 86 Sr limestone and ~ 60% from low- 87 Sr/ 86 Sr andesite. The stalagmite Sr/Ca and Ba/Ca ratios were higher than the ratio expected from the dissolved fraction of limestone and andesite. The covariance among Sr/Ca, Ba/Ca, and δ 13 C profiles suggests a significant role of prior calcite precipitation (PCP), i.e., carbonate precipitation from infiltrating water before the water drips on a stalagmite. The relationships among stalagmite Sr/Ca, Ba/Ca ratios and δ 13 C values are consistent with the Rayleigh-type fractionation model, supporting that PCP results in successive enrichment of Sr, Ba and 13 C in the aqueous phase and the resulting stalagmite. The degree of PCP calculated for the stalagmite is highly variable from 0 to 85%, and generally decreased from the last glacial period to the middle Holocene. The large degree of PCP observed during 18–15 ka implies a relatively dry climate during this period, which is consistent with weak monsoon intensity inferred by the δ 18 O values. The 87 Sr/ 86 Sr ratios of the stalagmite show a slight decrease through the entire period. The increase in the andesite-derived fraction with relatively high 87 Sr/ 86 Sr may result from accelerated silicate weathering in the epikarst with increasing temperature, humidity, and soil p CO 2 .